In shaft suspension units of this kind the shaft and parts connected thereto and rotating with the shaft during operation entrain the air or other gas, which is located in this space. This air or gas contains oil drops in the form of an oil mist, which is used to lubricate bearings arranged in the shaft suspension unit. By the rotation of the air the air pressure will be different in different parts of the space, which means that the air pressure as a rule is different at the two openings. This causes an often very high air flow in through the one opening and out through the other opening, whereby the oil drops are lost for their purpose and pollute the surroundings of the shaft suspension unit. Furthermore, particles, bacteria etc. might enter the shaft suspension unit and decrease the lifetime of the bearings or create colonies of bacteria.
In U.S. Pat. No. 4,654,023 there is shown a centrifugal separator with a shaft suspension unit, which has an opening through which the shaft of the centrifugal separator extends. At this opening there is arranged a mechanical sealing, which has a sealing element, which is connected to the shaft, and a sealing element, which is connected to a stationary outer casing of the shaft suspension unit, and which effectively prevents air or gas flow through the opening.
However, mechanical sealings of this kind are complicated, expensive and often consume a high effect. Furthermore, they are worn out quickly at the very high number of revolutions of centrifugal separators. Since they are difficult and time consuming to replace this involves high labour and downtime costs.